(1) Field of the Invention
The present invention relates generally to ovens for thermal treating a web and, more particularly, to an oven for thermally treating a textile fabric web having a model-based control system.
(2) Description of the Prior Art
Product quality is a primary concern of any manufacturing operation. In any process involving the application of heat, over exposure can be detrimental. For example, over exposure to heat of a textile web/fabric can cause yellowing, reduction in strength, harsh hand (feel of the product) and reduction in fastness properties. Likewise, under exposure can result in the purpose of the treatment not being accomplished for example, for a textile web, under exposure may result in a chemical reaction not going to completion, heat sitting not being accomplished, and/or fabric not being sufficiently dried. Heat treatment must also be uniform and consistent to have uniform and consistent quality.
In the textile industry, most ovens or other equipment used for the application of heat to a web utilize various proves, sensors and RTDs (remote temperature device) to sense temperature and to provide feedback information to a control system to maintain a desired temperature within the oven or other equipment. Manufacturing operations have used various devices to measure the temperature a product is exposed to in a particular process. In processing textiles, operators have typically used heat tapes (heat sensitive tape that can be attached to a web/product that changes color at a given temperature) to try to determent thermal exposure. Heat tapes are usually limited to identify a range of temperature, rather than a specific value, do not identify already processed materials.
IR measurement devices have also been used in the textile industry to both measure product exposure temperature and to provide sensor feedback information to a control system that interfaces with the speed of the process, so that speed can be modified and a desired product temperature can be maintained. However, practice has shown that the IR measurement devices have been difficult to maintain and keep in accurate calibration.
If conditions within the oven or heating equipment change, there is presently no equipment, mechanism or method to identify what has changed or what the effect may be on thermal exposure. There is no system of automation that can detect, identify the most likely cause for the changing conditions, and modify processing parameters to compensate for these changes, so that product thermal exposure and therefore quality can be maintained.
In addition to product quality, in the textile industry as well as other industries utilizing heat in the manufacturing process, the energy consumed has always been of concern, but in recent years, with a clearer realization of the finite resources available, there has been a greater effort to conserve energy. Generally, there are two major schools of thought regarding energy conservation in industry: (1) use less energy by operating, in the most energy efficient manner possible(theoretical analyses of process equipment, operating conditions and controls), and/or (2) recover effluent energy (energy leaving the process not consumed by the product).
The cost effectiveness of recovering effluent energy depends on the specific situation but, in many instances, the cost of the equipment to recover the energy involves a high capital investment and creates major maintenance difficulties. The energy that can be recovered is primarily low temperature, which has minimal usefulness, and some moderate temperature, which is more useful. Therefore, in practice, reducing consumption and optimizing processes to document energy consumption, developing instrumentation as necessary, to measure and then devise strategies for maximizing energy conservation for thermal finishing processes in use in the textile industry has proven to be the most fruitful approach.
One goal of a manufacturer is to operate using minimum resources to achieve maximum output, so that the unit cost is as low as possible and profit is maximized. Optimizing manufacturing processes has typically been done in a trial and error mode. Based on experience and laboratory testing, production variables have been identified and, if the desired quality of the end product has been achieved, then standards for production variables have been established. Improvements to a process have generally consisted of trials to refine the established parameters. Trials are costly in production machine time and in the materials consumed in running the trials, and whether or not true optimization has been achieved is not known. Typically, trials conducted on laboratory equipment cannot be directly transferred to production machines without additional production machine trials.
The interdependence and interconnectedness of the variables affecting thermal processing has not been accommodated by prior art control strategies devised thus far for equipment used in heat treating. Control systems typically focus on one variable, i.e., IR measurement of temperature and control of speed, measurement of moisture content in exhaust to control speed.
Thus, there remains a need for a new and improved oven for thermal treating a web, which provides model-based control while, at the same time, includes means for permitting a desired process profile to be transferred from one specific oven to another.
The present invention is directed to an oven for thermal treating a web. The oven includes: an oven chamber; a web transport for transporting a web through the oven chamber; heating means for heating the web in the oven chamber; an exhaust system connected to the oven chamber; and a model-based controller for controlling the web temperature profile. In the preferred embodiment, the model-based controller includes: (i) a plurality of sensor inputs; (ii) a plurality of control signal outputs; (iii) a multi-variable controller with first principles guidelines and oven and process boundaries for a first specific oven; (iv) a desired process profile; and (v) a translator module for permitting the desired process profile to be transferred to at least a second specific oven.
In the preferred embodiment, the oven further includes an air delivery system including at least one plenum having a plurality of air nozzles and a circulation fan. The air delivery system may include a pressure sensor system for determining thermal potential, such as a xcex94p sensor.
The oven chamber is generally conventional in design and includes an enclosed housing, a web entrance and a web exit. The web transport includes a web let-off means and a web take-up means for transporting the web through the oven. In addition, the web transport may further include a web mass monitor, such as a weight-speed monitor.
The heating means may be convection, radiant, or conduction heating. For example, in the preferred embodiment, the convection means is hot air heating. In addition, the radiant heating means may include infrared, radio frequency, or microwave heating and the conduction means may be a steam heat drum.
In the preferred embodiment, the model-based controller includes: a plurality of sensor inputs; a plurality of control signal outputs; a multi-variable controller with first principles guidelines and oven and process boundaries for a first specific oven; a desired process profile; and a translator module for permitting the desired process profile to be transferred to at least a second specific oven.
The sensor inputs receive measurements of web mass, heating temperature, exhaust rate, and web speed. In addition, the sensor inputs may further include a web mass sensor input. The plurality of control signal outputs may include a web speed control signal and/or a temperature control signal.
In the preferred embodiment, the multi-variable controller with first principles guidelines and oven and process boundaries for a specific oven further includes a model input for problem scenarios. In addition, it may further include a self-check module using a formula based lookup module.
Also, in the preferred embodiment, the translator module includes oven boundaries for at least a second specific oven and a boundary condition converter for producing new oven-specific boundaries for the second specific oven to attain the process profile.
Accordingly, one aspect of the present invention is to provide an oven for thermal treating a web. The oven includes: an oven chamber; a web transport for transporting a web through the oven chamber; heating means for heating the web in the oven chamber; an exhaust system connected to the oven chamber; and a model-based controller for controlling the web temperature profile.
Another aspect of the present invention is to provide a model-based controller for an oven for thermal treating a web, the oven including an oven chamber; a web transport for transporting a web through the oven chamber; heating means for heating the web in the oven chamber; and as exhaust system connected to the oven chamber. The model-based controller includes: a plurality of sensor inputs; a plurality of control signal outputs; a multi-variable controller with first principles guidelines and oven and process boundaries for a first specific oven; a desired process profile; and a translator module for permitting the desired process profile to be transferred to at least a second specific oven.
Still another aspect of the present invention is to provide an oven for thermal treating a web. The oven includes: an oven chamber; a web transport for transporting a web through the oven chamber; heating means for heating he web in the oven chamber; an exhaust system connected to the oven chamber; a model-based controller for controlling the web temperature profile, the model-based controller including: (i) a plurality of sensor inputs; (ii) a plurality of control signal outputs; (iii) a multi-variable controller with first principles guidelines and oven and process boundaries for a first specific oven; (iv) a desired process profile; and (v) a translator module for permitting the desired process profile to be transferred to at least a second specific oven; and an air delivery system.